More and more Department of Transportation (DOT) jurisdictions seek to create incentives for carpooling such as access to High Occupancy Vehicle (HOV) lanes on public highways. Such HOV lanes permit use only when a vehicle is being used to transport multiple occupants. One of the challenges with dedicating a lane to such “carpooling”, particularly in the introductory phase when there are not many carpoolers, is the resulting, and politically unpopular, increased congestion in the remaining, regular lanes.
To help mitigate this issue, many jurisdictions are introducing HOV lanes as High occupancy OR Toll (HOT) lanes to provide paid access to the lanes for single-occupant vehicles. While paid access to HOT lanes can be less democratic than access to lanes based solely upon occupancy, use of HOT lanes can be more politically acceptable. This is because overall traffic congestion resolution theoretically becomes self-regulating: some drivers will opt to pay a toll to access a reserved lane when congestion is high.
An additional carpooling incentive can take the form of access to private toll roads, with such access also being based upon paid admission. While carpooling can erode the profitability of toll highways, the availability of carpooling on private toll roads can help to alleviate overall traffic volume while simultaneously leading to lower road maintenance and lane expansion costs.
One of the biggest challenges in a municipality's introduction of a carpool lane is its being able to enforce a carpool occupancy requirement and, in the case of HOT lane access, knowing the identity of the party to be billed for single occupancy access. While technology exists to use photo confirmation to determine occupancy, these technologies often produce questionable confirmations that subsequently require human operator intervention post lane-access. Periodically, such technologies lead to incorrect billing, resulting in a costly and time-consuming review process.
Alternatively, drivers may employ transponder-based systems that require driver input prior to beginning a shared ride. Before approaching a verification point, a driver using a transponder system must remember to indicate carpool activity, usually by activating a switch on his transponder. In some cases the driver is required to switch off the transponder to force a “photo exception” to the existing transponder system. This reliance on driver input can lead to system failure in cases where a driver fails to timely or properly indicate carpool activity.